Crack resistant thermal spray alloy

ABSTRACT

The present disclosure provides a thermal spray alloy system that is more resistant to wear and/or corrosion than conventional alloy compositions. The disclosed alloys minimize or eliminate micro-cracks within the formed coating on the tool. The alloy comprises carbon, boron, and a fluxing agent selected from the group of aluminum, magnesium, or lithium. The alloy may also comprise titanium, silicon, manganese, molybdenum, nickel, and chromium, as well as other elements. The object to be coated may be any downhole component used in the oil and gas industry, or may be applied to any object or tool that needs an increased wear and/or corrosive protection layer including in diverse fields such as marine, chemical processing, and refining. A thermal spray coating with the disclosed alloy composition provides increased strength and resistance to spalling, breaking, cracking, deforming, and crack formation, as well as metallurgical bonding between the coating and the substrate.

PRIORITY

This application claims priority to U.S. provisional patent application No. 62/718,797, filed on Aug. 14, 2018, the entire contents of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to coatings applied to equipment and other substrates, and more particularly to thermally sprayed layers for increased protection for downhole equipment in oil and gas wells.

Description of the Related Art

Drilling wells for oil and gas recovery, as well as for other purposes, involve the use of drill pipes and other downhole equipment necessary for the exploration and production of oil and gas. Downhole equipment is exposed to severe abrasive wear conditions and corrosive environments. The most severe abrasive wear conditions occur when drilling through highly siliceous geological earth formations. A rotational movement of the pipe ensures the progression of drilling. Pipes commonly used today come in sections of about 30 feet or 45 feet in length. These sections are connected to one another by means of tool joints. These tool joints typically are connected to a center tube which is friction welded to the larger outer diameter (OD) tool joints. Because these tool joints are of larger outside diameter than the connecting tube they are subject to much more severe wear as they contact the open hole formations or the previously installed casing. Thus, these tool joints are generally protected against wear by abrasion resistant welded overlays. Further, any wear protection, whether welded or thermally spray, must be of low friction as it is rotated inside casing. This is called in the trade “casing friendly.” Should the drill string be rotated in place due to problems, and if it rotates against the casing wall in the same place, it is not uncommon for the drill string to wear through the casing causing a loss of circulation and well control. Such occurrences have been known to result in loss of the well and costing $100,000,000 in deepwater offshore wells. Therefore, wear resisting coatings must consider this possibility and by design have low friction especially at elevated temperatures of 250-500 F. Under conditions of vertical drilling the tool joints protect the body of the pipes quite efficiently. However, during handling the tool joints are often slammed into one another causing severe impact loading where most thermal spray coatings will spall.

More recent technology has evolved that utilizes directional drilling, meaning the deviation of drilling from vertical to horizontal over more or less large bending radiuses of curvature. This directional drilling also creates both compression and tension for lengths of the pipe during rotation. Coupled with the use of increased pipe section lengths of about 45 feet and larger diameters relative to the tool joint diameter, tool joints offer a lesser degree of protection of the body of the pipe and direct interaction of the pipe body with the walls of the well is more likely to occur. One consequence is an exposure of the pipe to wear mechanisms that may affect its integrity to a significant degree. When drilling into mineral formations, the wear mechanism involved is mainly abrasion. When drilling takes place into a steel casing or marine riser (where a marine riser connects a floating drilling or production unit to the wellhead(s) on the sea floor and through which the drill pipe passes), the wear mechanism is predominantly metal-to-metal wear with interposition of drilling fluids and drill cuttings. These wear situations are also encountered with other downhole equipment such as coiled tubing, downhole tools housing expensive instrumentation, and other components exposed to longitudinal and rotational wear during well drilling operations.

Because the tool joints have minimum OD acceptance criteria for safe use, they are typically hard banded. Hard banding is normally done by applying a single or double layer of hard metal by welding. The tool joints are made of forged, heat treated steels such as AISI 4137. This grade of steel is strong and tough but arc welding produces a heat affected zone under the weld layer which is much harder and is subject to hydrogen assisted cracking and sulfide stress corrosion cracking. While this standard “hard banding” practice generally resists wear in many applications, it does cause the introduction of heat into the tool joint which causes (among other negative side effects) unintended degradation of the internal plastic of epoxy coating. As is known in the art, most drill pipe is coated internally with a corrosion resistant epoxy to prevent corrosion and reduce friction of the drilling fluids. This coating can withstand up to 400 F before degradation. Welding raises the temperature to about 700 F and thus burns this coating off leaving the interior surface of the tool joint without corrosion protection.

Many drill strings and especially those involved in extended reach drilling have tools near the bit that communicate to the surface via sonic pulses through the drilling fluid. An advanced design of drill pipe, known in the art as wired pipe and by the brand name Intellipipe, has an electrical or fiber optic or other communication cable running along its length and having a special device for transferring the signals in the tool joints such that when joints of pipe are screwed together the communication transfers. This communication system is sensitive to the heat of welding and in order to re-hard band the tool joints, the entire system must be removed, then re-installed after welding and re-tested.

As is known in the art, the term “thermal spray” is a generic term for a group of processes in which metallic, ceramic, cermet, and some polymeric materials in the form of powder, wire, or rod are fed to a torch or gun with which they are heated to near or somewhat above their melting point. The resulting molten or nearly molten droplets of materials are projected against the surface to be coated. Upon impact, the droplets flow into thin lamellar particles adhering to the surface, overlapping and interlocking as they solidify. The total coating thickness is usually generated in multiple passes of the coating device; depending on the application, the layer may be applied in thick deposits exceeding 0.100,″ although ranges in the amount between 0.020″ up to 3.0″ are possible. Various thermal spray techniques may include flame spraying, flame spray and fuse, electric-arc (wire-arc) spray, and plasma spray. Thermal spray may be applied to a wide variety of tools, equipment, structures, and materials, and is not limited to merely downhole components. Thermal spray with special alloys is applied to drill pipe, casing, sucker rods and other components used in the drilling, completion and production of oil and natural gas. Among other benefits, this application is used to mitigate wear, reduce friction, and to create a standoff from the annulus of the hole.

The prior art discloses various methods for thermal spraying. For example, U.S. Pat. No. 7,487,840 (“the '840 patent”), incorporated herein by reference, discloses a protective wear coating on a downhole component for a well through a thermal spraying process in combination with an iron-based alloy. Likewise, U.S. Pat. No. 9,920,412 (“the '412 patent”), incorporated herein by reference, discloses a similar thermal spray technique with a chromium free composition of thermally sprayed material. As discussed in the '840 patent, the thermal spraying process melts the material to be deposited while a pressurized air stream sprays the molten material onto the downhole component. The coating operation takes place at low temperatures without fusion or thermal deterioration to the base material. The wear resistance is increased while providing a lower coefficient of friction by the wear resistant layer relative to a coefficient of friction of the downhole equipment without the wear resistant layer. FIG. 3 of the '840 patent is reproduced in the present disclosure as FIG. 1A as an exemplary thermal spraying process that may be used in conjunction with the present invention. The following two paragraphs describe FIG. 3 of the '840 patent are reproduced from the specification of the '840 patent at column 6, 11. 3-27:

“FIG. 3 [reproduced as FIG. 1A in the present disclosure] is a schematic diagram of an exemplary thermal spray system for applying a wear resistant layer to a downhole component, according to the present invention. One type of thermal spraying system 30 that is advantageously used is a twin wire system. The twin wire system uses a first wire 32 and a second wire 34. In at least one embodiment, the first wire 32 and the second wire 34 generally are of the same nature, whether solid or tubular, and the same diameter, but not necessarily of the same chemical composition. For example, the first wire 32 could be of a first composition, while the second wire 34 could of the same or a complementary composition to the first composition to yield a desired wear resistant layer on the base material.”

“A voltage is applied to the wires. The proximity of the wire ends creates an arc 35 between the ends and cause the wires to melt. A high-pressure compressed air source 36 atomizes molten metal 38 caused by the arcing into fine droplets 40 and propels them at high velocity toward the downhole component, such as conduit 10 or other components, to being deposited on the external surface 26. The twin wire spraying process can use commercially available equipment, such as torches, wire feeding systems and power sources. Other thermal spraying processes are available and the above is only exemplary as the present invention contemplates thermal spraying processes in general for this particular invention.”

While conventional thermally sprayed layers (such as that disclosed in the '840 patent and the '412 patent and other literature) are useful in numerous instances, such compositions are not helpful in many environments, whether for corrosive and/or wear resistant applications. For example, these prior art techniques (and thermal spray alloys) have not addressed the tool joint hard banding areas and have failed when the coating spalls off due to corrosion or poor application resulting in a weak bond with the pipe surface. As another example, in certain applications (such as on drill pipe and tools that are subject to severe flexing, torque and impact) they fail because the sprayed metal is brittle and develops cracks 131 (see, e.g., FIG. 1C) that propagate in fatigue loading. In particular, a significant part of the coating applied to drill pipes using conventional thermally sprayed layers may be “spalled” off and/or otherwise broken into smaller pieces, as shown for example in FIG. 1B. Such spalling 121 (FIG. 1B) significantly reduces the benefits of the coated layer and in many instances makes the drill pipe unusable for the intended application. Thus, conventionally thermally sprayed layers have not been dependable for drill pipe and are subjected to breaking, cracking, deforming, etc. under various applications.

A contributing factor to crack propagation and spalling is the inherent presence of micro-cracks in the coating. During use coatings on drill pipe are subjected to impact, torsion, and fatigue which causes these micro-cracks to open to the surface. A crack open to the surface of the coating will open and close during the rotation of the pipe as the pipe bows and alternately subjects the coating and open crack to tension and compression or opening and closing with each rotation. Because coatings are brittle the cracks will open further from pure fatigue, from hydraulic pressures from the drilling fluids, and over time from corrosion from the presence of hydrogen sulfide and chloride salts. These cracks grow downward to the interface of the coating with the pipe surface and then move axially to the pipe until a patch of the coating is dis-bonded and falls out. These micro-cracks are particularly problematic in thermal spray deposits thicker than 0.015.″

The statements in this section are intended to provide background information related to the invention disclosed and claimed herein. Such information may or may not constitute prior art. It will be appreciated from the foregoing, however, that there remains a need for an improved method, device, and system for thermally sprayed layers that are more resistant to cracking, breaking, and/or failure. A need exists for an improved method and system for thermally sprayed layers on downhole components that is more impact resistant, wear resistant, and/or corrosion resistant, and/or is otherwise more durable than existing thermally sprayed layers. A need exists for an improved method and system for thermally sprayed layers that are more resistant to corrosion, mitigate wear, and lower friction. A need exists for a new alloy that provides enhanced corrosion resistance, wear resistance, and lowered friction. Such disadvantages and others inherent in the prior art are addressed by various aspects and embodiments of the subject invention.

SUMMARY OF THE INVENTION

The present disclosure provides a thermal spray alloy system that is more resistant to wear and/or corrosion than conventional alloy compositions. The disclosed alloys minimize or eliminate micro-cracks within the formed coating on the tool. The alloy comprises carbon, boron, and a fluxing agent selected from the group of aluminum, magnesium, or lithium. The alloy may also comprise titanium, silicon, manganese, molybdenum, nickel, and chromium as well as other elements. The object to be coated may be a downhole component or other tool used in the oil and gas industry (such as hard banding for drill pipes), or may be applied to any object or tool that needs an increased wear and/or corrosive protection layer including in diverse fields such as marine, chemical processing, and refining. A thermal spray coating with the disclosed alloys provides numerous benefits, including increased strength and resistance to spalling, breaking, cracking, deforming, crack formation, and corrosion, as well as metallurgical bonding between the coating and the substrate.

Disclosed is a composition for thermally spraying to a substrate, wherein the composition comprising iron alloyed with the following components: at least 0.3 wt % carbon, at least 5.0 wt % boron, and at least 0.5 wt % of a fluxing agent selected from the group consisting of aluminum, magnesium, or lithium. The composition may comprise at least 0.5 wt % lithium, at least 0.5 wt % magnesium, and/or at least 0.5 wt % aluminum. Likewise, the composition may comprise at least 5.0 wt % lithium, at least 5.0 wt % magnesium or at least 5.0 wt % aluminum. In one embodiment, the composition may comprise at least 2.0 wt % aluminum and at least 0.5 wt % lithium. In other embodiments, the composition may comprise at least 1.0 wt % titanium, at least 0.5 wt % carbon, and/or at least 7.0 wt % boron. In other embodiments, the composition may further comprise at least 2.0 wt % aluminum, at least 1.0 wt % nickel, and at least 1.0 wt % titanium. In one embodiment, the composition may further comprise a plurality of reactants that create an exothermic reaction when ignited and thermally sprayed onto the substrate. For example, the plurality of reactants may comprise aluminum and iron oxide, such that the amount of aluminum to iron oxide is approximately 1-part aluminum to 3-parts iron oxide. Other reactants may be utilized. In other embodiments, lithium and iron oxide may be used, magnesium and copper oxide may be used, or in general any oxide and a metal may be used that is effective to create an exothermic reaction to produce the desired results described herein.

In one embodiment, the amount of the fluxing agent is effective to increase droplet temperature of the composition during thermal spray. In another embodiment, the composition is effective to cause metallurgical bonding between a layer of sprayed metallic material and the substrate. In another embodiment, the composition is effective to prevent micro-cracks from forming in the thermal spray. In another embodiment, the composition is effective to reduce the amount of micro-cracks within a layer of sprayed metallic material on the substrate. In another embodiment, the composition is effective to diffuse at least a portion of the carbon and boron to a base material of the substrate.

Disclosed is a modified downhole component that comprises an external surface and a layer of metallic material that is thermally sprayed onto a portion of the external surface. In one embodiment the layer of metallic material comprises a composition, at least prior to being sprayed, of at least 0.3 wt % carbon, at least 5.0 wt % boron, and at least 0.5 wt % of a fluxing agent selected from the group consisting of aluminum, magnesium, or lithium. In one embodiment, the composition comprises at least 2.0 wt % aluminum and/or at least 0.5 wt % lithium. The component may be a wide variety of tools or objects, and may be a drill pipe or a drill pipe tool joint. In one embodiment, at least a portion of the carbon and boron has diffused from the layer of metallic material to a base material of the downhole component.

Disclosed is a modified downhole component that comprises an external surface and a layer of metallic material that is thermal sprayed onto a portion of the external surface, wherein the layer of material is at least partially metallurgically bonded to the downhole component. In one embodiment the layer of metallic material comprises a composition, at least prior to being sprayed, of at least 0.3 wt % carbon, at least 5.0 wt % boron, and at least 0.5 wt % of a fluxing agent selected from the group consisting of aluminum, magnesium, or lithium.

A layer of the sprayed metallic material may have a wide range of thicknesses. In one embodiment, the layer of metallic material has a thickness of between about 0.010 inches and 0.10 inches. In another embodiment, the layer of metallic material has a thickness of between about 0.10 inches and 1.0 inches. In still another embodiment, the layer of metallic material has a thickness of between about 1.0 inches and 3.0 inches.

In one embodiment, the layer of the sprayed metallic material is resistant to micro-cracks and/or has substantially no micro-cracks. In one embodiment, layer of metallic material is at least partially metallurgically bonded to the downhole component. In one embodiment, the layer of metallic material is formed by an exothermic reaction. In one embodiment, the downhole component comprises one or more reinforcing structures embedded within the layer of metallic material. For example, the one or more reinforcing structures may comprise one or more continuous wires or a plurality of whiskers.

Disclosed is a method for thermally applying a coating to a substrate that comprises thermally spraying metallic material on an external surface of a substrate to form a thermal spray layer on the substrate, wherein the material, at least prior to being sprayed, comprises iron alloyed with the following components: at least 0.3 wt % carbon, at least 5.0 wt % boron, and at least 0.5 wt % of a fluxing agent selected from the group consisting of aluminum, magnesium, or lithium. In one embodiment, the method further comprises embedding one or more reinforcing structures into the thermal spray layer. In one embodiment, the method further comprises the one or more reinforcing structures onto the external surface of the substrate by compressed gas. In one embodiment, the method further comprises metallurgically bonding the sprayed metallic material with the substrate. In one embodiment, the method further comprises metallurgically bonding together droplets of the sprayed metallic material. In one embodiment, the method further comprises increasing droplet temperature of the sprayed metallic material by using a lithium compound. In one embodiment, the method further comprises diffusing boron and carbon between the thermal spray layer and the substrate. In one embodiment, the method further comprises creating an exothermic reaction during the thermal spray step. In one embodiment, the method further comprises igniting a plurality of reactants within a cored wire to create the exothermic reaction. In one embodiment, the method further comprises forming a layer of thermally sprayed material on the substrate that is between about 0.010 inches and 0.10 inches, at least 0.1″ thick, or at least 1.0″ thick.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein.

FIG. 1A illustrates one prior art method of thermally spraying a downhole component, which is taken from FIG. 3 of U.S. Pat. No. 7,487,840.

FIG. 1B illustrates a photograph of a drill pipe with a conventional thermally sprayed layer with portions of the layer “spalled” and/or otherwise broken/fragmented off.

FIG. 1C illustrates a photograph of a typical crack formed in a weld.

FIGS. 2A and 2B illustrate one schematic of a typical drill pipe with tool joints.

FIG. 3A illustrates a cross-sectional view of a thermally sprayed sample of Alloy 1 according to the present disclosure, at a magnification of 444×.

FIG. 3B illustrates a cross-sectional view of a thermally sprayed sample of Alloy 2 according to the present disclosure, at a magnification of 444×.

FIG. 3C illustrates a cross-sectional view of a thermally sprayed sample of Alloy 3 according to the present disclosure, at a magnification of 444×.

FIG. 3D illustrates a cross-sectional view of a thermally sprayed sample of Alloy 4 according to the present disclosure, at a magnification of 444×.

FIG. 4A illustrates an elemental composition breakdown in the base material of a substrate after being thermally sprayed with Alloy 3.

FIG. 4B illustrates an elemental composition breakdown at the interface between the base material of a substrate and the thermal spray droplets of Alloy 3.

FIG. 4C illustrates an elemental composition breakdown in the thermal spray deposit of Alloy 3 after spraying and after the droplets become splats.

FIG. 5A illustrates a cross-sectional view of a thermally sprayed sample of Alloy 4, at a magnification of 1200×.

FIG. 5B illustrates an elemental composition breakdown of the sample from FIG. 5A.

FIG. 6A illustrates a cross-sectional view of a conventional thermally sprayed coating without using an exothermic reaction, at a magnification of approximately 69×.

FIG. 6B illustrates a cross-sectional view of a thermally sprayed coating according to one embodiment of the present disclosure (showing no cracks) using an exothermic reaction, at a magnification of approximately 69×.

FIG. 7 illustrates a cross-sectional view of a thermally sprayed coating according to one embodiment of the present disclosure (showing metallurgical bonding) using an exothermic reaction, at a magnification of approximately 7000×.

DETAILED DESCRIPTION

Various features and advantageous details are explained more fully with reference to the nonlimiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known starting materials, processing techniques, components, and equipment are omitted so as not to unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the invention, are given by way of illustration only, and not by way of limitation. Various substitutions, modifications, additions, and/or rearrangements within the spirit and/or scope of the underlying inventive concept will become apparent to those skilled in the art from this disclosure. The following detailed description does not limit the invention.

Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

Overview

The present disclosure provides a novel thermal spray alloy. In particular, at least four separate alloys have been designed and tested and are specifically disclosed herein. Other alloys have also been tested and elemental compositions varied and studied for the purposes of the present disclosure. The disclosed alloys provide superior benefits to conventional thermal spray techniques and alloys utilized therein. For example, the disclosed alloys minimize and/or eliminate micro-cracks that are typically inherent in typical thermal spray techniques and/or alloys. In one embodiment, the disclosed alloys minimize and/or eliminate micro-cracks while retaining wear resistance, friction reduction, and/or corrosion resistance in thicker deposits (e.g., greater than 0.02″ and more particularly greater than approximately 0.1″) of thermally sprayed materials.

Further, use of various elements can increase the diffusivity rate of particular components, such as boron and/or carbon, across the thermal spray droplet interfaces and into the base material of the substrate. The alloy may comprise a fluxing agent as defined herein, such as aluminum, lithium, or magnesium, which functions as a very reactive element for the overall alloy composition and thermal spray reaction. In one embodiment, the fluxing agent is effective to prevent oxide formation on droplets of the thermally sprayed metallic material and is used in combination with an exothermic reaction to increase metallurgical bonding, enhanced elemental diffusion to the substrate, and crack prevention. The alloy may also comprise silicon, titanium, nickel, molybdenum, and/or chromium. Iron may form a majority portion of the alloy composition. While the disclosed alloys are useful for any downhole equipment, in one embodiment they are particularly useful for drill pipe, and in particular drill pipe tool joints.

In one embodiment, the disclosed alloy provides numerous benefits superior to conventional thermally sprayed alloys, including increased wear and corrosion resistance. For example, the disclosed alloys are robust and provide sufficient wear and corrosion resistance to be applied successfully to the hard band area of tool joints on drill pipe.

In one embodiment, the form of the spray material is a cored wire, in which may comprise an outer sheath that substantially encloses powdered material. As is known in the art, the inner core comprises the powdered ingredients of the alloy, and include powdered materials such as borides, carbides, tin, iron oxide, aluminum, etc. The making of such outer sheaths and inner cores of the cored wire is known to those of skill in the art. In other embodiments, the disclosed alloy can be produced as a solid wire. In still other embodiments, the disclosed alloy may be applied as a powder.

Table I below provides various exemplary ranges of the elemental compositions of the disclosed alloy system, which may be part of a cored wire system. In one embodiment, the listed compositions of the alloy are prior to the alloy being sprayed. Thus, some of the below elemental components may be located within an outer sheath of the cored wire (such as nickel), while other elemental components may be located within an inner core of the cored wire (such as boron, carbon, etc.). Table I also provides exemplary compositions of different specimens of the disclosed alloys.

TABLE 1 Elemental Compositions (Percent by Weight) Element Alloy 1 Alloy 2 Alloy 3 Alloy 4 Carbon   0.53 0.50 0.70 0.34 Manganese -0- 0.32 0.24 2.48 Silicon -0- 0.21 0.34 0.62 Boron   7.07 7.07 6.62 4.77 Aluminum   2.0 2.0  3.61 2.04 Nickel -0- 0.16 4.98 1.80 Molybdenum -0- -0-   -0-   1.25 Chromium -0- 11.27  4.50 -0-   Titanium   1.4 1.4  2.25 1.47 Lithium -0- -0-   1.16 -0-   Iron Balance Balance Balance Balance

One of ordinary skill will realize that each of the components may vary in composition and achieve the same or similar results as described herein. In other words, other variations and elemental compositions are possible within the scope of this disclosure, depending on the particular substrate being applied and desired properties of the coating and corrosion/wear resistant layer. Further, some of the above elements (or other elements) may exist in the composition in a trace amount (or approximately 0%). In other words, if not listed above (or if listed as “-0-”), the particular element was not intentionally added to the alloy and exists in a trace amount (e.g., less than 0.02 wt %).

In one embodiment, each of the disclosed alloys has a majority percentage by weight of iron. In other embodiments, iron may not be used. In one embodiment, if a particular element is utilized, the composition may comprise about 0.30 to 0.70 wt % carbon, about 0.20 to 2.50 wt % manganese, about 0.20 to 0.75 wt % silicon, at least 5.0 wt % boron and more particularly about 4.5 to 7.5 wt % boron, at least 2.0 wt % aluminum and more particularly about 2.0 to 4.0 wt % aluminum, about 0.1 to 5.0 wt % nickel, about 1.00 to 1.50 wt % molybdenum, about 4.0 to 12.0 wt % chromium, about 1.4 to 2.5 wt % titanium, and/or about 1.0 to 2.0 wt % lithium. In one embodiment, the composition may comprise at least 1% by weight of lithium, at least 1.0% by weight of titanium, at least 4.5% by weight of chromium, at least 1.0% by weight of molybdenum, at least 2.0% by weight of aluminum, at least 5% by weight of boron, at least 0.20% by weight of silicon, at least 0.20% by weight of manganese, and/or at least 0.30% by weight of carbon.

In one embodiment, Alloys 1-4 utilize aluminum. In some embodiments, magnesium or lithium may be used in lieu of or in addition to aluminum. In one embodiment, the present disclosure utilizes a fluxing agent to help minimize the formation of harmful compounds (oxygen, hydrogen, etc.) during a thermal spray process. A fluxing agent, for the purposes of the present disclosure, is a very powerful oxidizer and also reacts with other metallurgically harmful elements such as hydrogen, nitrogen, and chlorine, all of which are detrimental to iron and nickel based alloys. As is known in the art, hydrogen is well known to cause cracking, including micro-cracks in iron based alloys. Further, it is well known in the art that oxygen combines with a variety of elements such as iron, silicon, manganese, chromium, titanium, aluminum to form brittle phases that can be fracture initiation sites or fracture paths. These oxides also deter alloys or elements from joining together, such as the solidifying droplets experience in the thermal spray processes. Thus, it is beneficial to remove or reduce the oxide formation on the droplet surface, which promotes metallurgical bond strength and thus ductility of the coating. For example, lithium compounds have been used as fluxing agents in the manufacture of steel, such as disclosed in U.S. Pat. No. 3,942,977, incorporated herein by reference. In one embodiment, the use of aluminum, magnesium, and/or lithium in the alloy composition are beneficial in the prevention of micro-cracks by preventing oxides of iron and/or silicon. In one embodiment, the droplet surfaces are protected from having an oxide film which is a brittle phase and is more crack prone. Further, oxides have poorer wear resistance in abrasion as they easily fracture and fall out on a micro scale.

In one embodiment, aluminum, magnesium, or lithium may be used as the fluxing agent. Lithium is well known to be a very reactive metal. For example, lithium is known to be more reactive than potassium, sodium, magnesium, aluminum, zinc, iron, and other metals. In one embodiment, lithium is more reactive than both aluminum and magnesium, and thus may be the most aggressive or best fluxing agent as compared to magnesium and aluminum. In one embodiment, the extreme reactivity of lithium (or the other fluxing agents of magnesium and aluminum) is important to achieve a successful reaction during a thermal spray process. During a typical thermal spray process, wires are melted and metallic material is atomized and sprayed onto a substrate. The atoms endure a very brief time of flight before striking the substrate, flattening out on the substrate, and solidifying on the substrate. Thus, the available reaction time for a thermal spray alloy composition is very short. While aluminum and magnesium metals may be used instead of lithium to enhance a reaction, they are not as reactive as lithium and they are much slower at generating heat than lithium.

In one embodiment, Table II provides sample elemental compositions of various embodiments of the alloy of the present disclosure utilizing a fluxing agent. The percentages illustrated in Alloys 5-7 are minimal compositions for the listed elements, and the percentages listed in Alloy 8 are exemplary ranges for the listed elements. Similar to the compositions listed in Table I, one of skill will recognize that other variations and elemental compositions are possible within the scope of this disclosure.

TABLE II Sample Elemental Compositions (Percent by Weight) Element Alloy 5 Alloy 6 Alloy 7 Alloy 8 Carbon   0.30   0.50   0.70 0.3-0.7 Manganese -0- -0- -0- 0.0-2.5 Silicon -0- -0- -0- 0.0-1.0 Boron   5.0   6.0   7.0 3.0-8.0 Nickel -0- -0- -0- 0.0-5.0 Molybdenum -0- -0- -0- 0.0-1.5 Chromium -0- -0- -0-  0.0-15.0 Titanium -0- -0- -0- 0.0-2.5 Lithium   -0.5- -0- -0- 0.0-5.0 Aluminum -0-   -2.0- -0- 0.0-5.0 Magnesium -0- -0-   -5.0- 0.0-5.0 Iron Balance Balance Balance Balance

In one embodiment, the disclosed alloy may have a fluxing agent (such as aluminum, magnesium, or lithium) that comprises at least 0.5% or less of the overall composition, and may be 5.0% or more of the overall composition. In one embodiment, the fluxing agent may be magnesium at approximately between 0.5 and 5.0 weight percent of the composition, such as approximately 1.0 weight percent. In one embodiment, the fluxing agent may be aluminum, and may comprise approximately 0.5 to 5.0 weight percent of the alloy composition, such as approximately 2.0 weight percent. In one embodiment, the fluxing agent may be lithium, and may comprise approximately 0.5 to 5.0 weight percent of the alloy composition. In other embodiments, the composition may comprise multiple fluxing agents, such as aluminum and lithium, aluminum and magnesium, or magnesium and lithium. For example, in one embodiment, the composition may comprise at least 0.5 weight percent lithium and at least 2.0 weight percent aluminum. In one embodiment, the alloy may comprise at least 0.30 weight percent carbon and at least 5.0 weight percent boron. Titanium may or may not be used. In one embodiment, the composition may comprise at least 1.0% weight percent titanium. Other elements may be used as disclosed above in relation to Table I and the sample elemental ranges as disclosed in Alloy 8 in Table II.

In one embodiment, the alloy composition may comprise lithium. To the Applicant's knowledge, no other alloy for thermal spray application utilizes lithium as part of the composition of a thermal spray alloy. As described above, Alloy 3 comprises at least 1.0% lithium, Alloy 5 comprises at least 0.5% lithium, and Alloys 8 comprises up to approximately 5.0% lithium. In one embodiment, lithium may be added to the disclosed thermal spray alloy composition in the amount of at least 0.5 weight percent, while in other embodiments lithium may be added up to approximately 5.0 weight percent. As described herein, the Applicant has conducted tests with and without lithium (see Alloy 3, see also FIGS. 4A-4C and FIG. 6B), and has discovered that thermal spray alloy compositions comprising lithium produce products that have greater metallurgical bonding, enhanced carbon and boron diffusion, and minimization of micro-cracks. In one embodiment, the use of lithium increases the reactivity of the other components and/or the chemical reaction and increases the temperature of the reaction, thereby promoting better diffusion and bonding. In one embodiment, the present disclosure utilizes lithium as a fluxing agent to help minimize the formation of harmful compounds (oxygen, hydrogen, etc.) during a thermal spray process. While lithium compounds are well known as a fluxing agent in the production of steel, copper, and nickel alloys, they are not used in conventional thermal spray processes. In one embodiment, lithium is used as an element to increase the temperature of the reaction of metallic components during the thermal spray process. As described below, exothermic reactions during a thermal spray process provide numerous benefits. In one embodiment, the oxidation of lithium is exothermic which contributes to the super heating of the thermal spray droplets in the molten state. As described above, other fluxing agents such as aluminum and magnesium may also be used to increase the temperature of the reaction, although these other elements may not increase the temperature as much or as fast as a lithium compound.

Various forms or compounds of lithium may be used. In one embodiment, lithium may be added to the alloy composition as a substantially pure metal or metallic compound, such as lithium copper or lithium aluminum. However, lithium as a pure metal or metallic compound is very reactive with oxygen and water (e.g., moisture), which may be problematic during a typical thermal spray process. In other embodiments, a more stable lithium containing compound may be used, such as lithium fluoride, lithium oxide, or lithium carbonate. In one embodiment, these lithium compounds decompose readily in the thermal spray arc releasing lithium to act as a fluxing agent.

If a cored wire is utilized, one or more of materials may be located within an inner core of a cored wire, such as carbon and/or boron. In one embodiment, the composition may further comprise powdered compositions of carbon, iron, titanium, aluminum, magnesium, and/or manganese. The fluxing agent may or may not be located within the inner core of the cored wire.

In general, each element of the alloy is an important part of the disclosed alloy composition: relatively small weight changes to one component might make significant changes to the overall performance effects of the alloy, while relatively large weight changes to one component might cause relatively minor changes to the overall performance of the alloy. While many of these elements are well known for thermal spray alloys, the disclosed ranges and combinations are unique for an alloy and, to the Applicant's knowledge, previously never been made and/or utilized as a thermal spray alloy. On the other hand, some of these elements are not typical for a thermal spray alloy. For example, to the Applicant's knowledge, no other alloy for thermal spray application utilizes lithium as part of the composition of a thermal spray alloy.

Thermal Spray Coating

As shown in FIG. 1A (reproduced from the '840 patent), metallic droplets 40 are deposited onto an external surface 26 of tool 10 by thermal spraying system 30. One or more thermal spray layer(s) is formed on the external surface of the tool by the metallic droplets and is coupled to the external surface of the tool. A resulting coating 24 is provided on the external tool surface that comprises the thermal spray layer. Among many other benefits, this coating is more resistant to impact and wear and provides a friction reduction layer to the tool and is considered more durable than prior art thermally sprayed alloys.

In general, a “wear resistant layer” and/or durable coating as discussed herein is a coating of material dissimilar to the pipe or tool material being coated that may range between 0.020″ and 3.0″ of thickness that substantially lowers wear on the tool and produces less friction than the conventional base material (e.g., bare steel). The coating may also provide beneficial stand-off of the component from the annulus.

In one embodiment, the thermal spray coating does not cause significant metallurgical effects on the base material of the component and does not raise the temperature of the base material sufficiently to cause thermal damage to typical internal coatings, for example, on instrumentation and other downhole components.

As mentioned above, the resulting coating provides numerous benefits compared to prior art thermally sprayed layers and the characteristics of the coating may be variable based on the intended application, desired results, and substrate being coated. For example, a coating of the present disclosure may provide not only a far superior wear surface compared to other types of applied coatings, such as—paint, epoxy coating, and powder coatings, but also provides a significantly increased impact resistant layer of thermal spray as well as corrosion resistant thermally sprayed overlays.

In general, the thermal spray coating is repairable, and the downhole component can be repeatedly recoated with the thermal coating process disclosed herein. For example, a first thermally sprayed layer may be applied to the surface, and a second thermally sprayed layer (which may be the same or different than the first layer) may be applied over the first layer. The coating resists spalling or otherwise peeling off and provides a surface that is much more resistant to impact and/or damage than prior applications of thermal spraying.

Application

In one embodiment, the disclosed alloy is applied to components that are subject to friction, wear, and/or corrosion damage. The disclosed alloy is readily applied using thermal spray application methods. In one embodiment, the relevant components are downhole oil well production components such as drill pipes and tool joints. However, the disclosed alloys will be beneficial in other non-downhole markets where severe friction, wear, and/or corrosion is present.

As mentioned above, drill pipe and tool joints may be protected by a weld or thermal spray hard banding, and the disclosed thermal spray alloys are particularly suitable for drill pipe tool joints. The below features are a few of the benefits provided by the disclosed alloys. In general, while conventionally thermally sprayed alloys try to address some of these features, they fail to address them sufficiently.

In general, a thermal spray overlay on drill pipe should have some or all of the following protection attributes: protects drill pipe from tool joint wear, protects drill pipe from mid-tube wear, protects drill pipe from internal corrosion of tool joints by preserving the internal plastic coating, reduces fatigue in drill pipe tube that can cause failure, reduces risk of buckling due to mid-tube stand-off and lower friction, reduces vibration of drill string increasing weight on bit, protects casing from wear, protects casing better than welded hard banding due to surface roughness of welds compared to thermal spray (which has relatively smooth surfaces), protects risers from wear, and/or lowers friction in riser. Based on these attributes, fewer inspections of drill pipe is required as long as the sacrificial thermally sprayed areas are not worn down to the pipe or tool joint steel.

In general, a thermal spray overlay on drill pipe should have some or all of the following performance enhancing attributes: lowers friction, thus increases rate of penetration (ROP) as coating has lower friction than steel—it slides easier; reduces the need for expensive lubricants in the drilling mud; offers increased standoff (by the use of mid-tube bands) from the pipe tube to the casing or formation thereby reducing curvature of the pipe in the lateral section and thus increasing weight on bit; and reduces the contact area of the tube to open hole formation and casing by the use of mid-tube bands acting as sleeve-bearings. In some embodiments, if ribs, instead of bands, are used, the curved ribs act as hole cleaners, thereby stirring up the cuttings bed in the lateral section of the bore hole. In other embodiments, the use of ribs or bands substantially lowers the risk of differential sticking by reducing the contact area. Differential sticking is problematic for drillers, as the drill string cannot be moved when stuck. If the potential for differential sticking is expected the driller will add a tool known as a “jar” to the drill string. When actuated, the jar induces a violent shock to the drill string to try and break it free. Jars are expensive, may not work, and are known to cause damage to the bottom hole assembly.

FIG. 2A illustrates one schematic of a typical drill pipe with tool joints. In one embodiment, tool joint 201 comprises a threaded male end 205 (known as the pin) and a threaded female end 203 (known as the box). Portions of the tool joint may be protected with thermal spray wear bands, such as bands 211. In one embodiment, as illustrated in FIG. 2B, portions of the tool joint (such as a pin tool joint 221) have tapers with certain angles, such as approximately 30 degrees. The disclosed alloy may be sprayed on these portions to not only increase the wear resistance on this section but to reduce the angle. For example, as illustrated in FIG. 2B, one or more layers of thermal spray may be coated on the angled portion of a pin tool joint to form a coating 223, which reduces the angle from approximately 30 degrees to about 15 degrees. Among other benefits, this reduces damage to the MPD seal when tripping out of the hole.

In one embodiment, the disclosed thermal spray alloy can be applied easier than welded hard banding. In some situations, welding cannot be employed on the tube of the drill pipe due to large induced stresses, thereby weakening the steel. Further, thermal spray can be applied to more precise thicknesses than arc welding overlays.

In one embodiment, thermal spray of the disclosed alloys can be applied in thin layers, such as about 0.005″, whereas welding cannot be applied this thin. Thin layers allow the coating of the entire tool joint outside diameter in a thin layer to further enhance wear resistance. Further, the thermal spray layer can be “tonged on” as it will compress slightly allowing gripping where weld overlays of hard metals will not deform and thus cannot be tonged on. This means that once the normal hard band has worn down to the level of the coating on the entire tool joint that the wear would slow as there is much more contact area to carry the load.

In one embodiment, a thermal spray utilizing the disclosed alloys can successfully be applied to many base metal alloys including steel, stainless steel, nickel alloys, titanium alloys, aluminum alloys, copper alloys, magnesium alloys and even non-metals such as fiberglass and composites. In contrast, welding alloys must be carefully designed for each metal.

In one embodiment, a thermal spray utilizing the disclosed alloys (such as by twin wire arc spray) is performed below 300 F. These relatively low temperatures do not create a heat affected zone to the pipe and are not detrimental to any internal epoxy coating. Further, low temperatures allow thermal spray to be applied to drill pipes with communication systems (e.g., wiring) without harming the communication systems and other electronics. Thus, drill pipe sections and other communication systems need not be removed, replaced, and re-tested at each link of each joint of pipe. This is a considerable time and costs savings compared to traditional welding techniques on drill pipes, including with thermal spray techniques.

While an embodiment of the disclosure is directed to drill pipe or other downhole components used in the oil and gas industry, a thermally sprayed layer of the disclosed novel alloy can be used in a variety of applications and industries. For example, the disclosed wear resistant thermally sprayed layer may be used for many other downhole components in the oil and gas industry, such as but not limited to drill pipes, drill pipe tool joints, heavy weight pipes, stabilizers, cross-overs, jars, MWDs, LWDs, drill bit shanks, etc. The disclosed wear resistant thermally sprayed layer may also be used on objects other than downhole components where an increased wear and/or corrosion resistant layer is needed, such as dredge pups, cable sheaves, helicopter landing runners, etc., including the automotive, aviation, and marine industries. The disclosed wear resistance layer may also be used on banding to rigidly attach separate components, such as around drill pipe tool joints.

The process of thermal spray is well known to those of skill in the art. Thermal spray is a flexible process and can be applied to a wide variety of substrates and/or surfaces, such as irregular, tubular, or flat surfaces and to virtually any metal or non-metal substrate. In general, the process involves cleaning the substrate and forming a rough surface profile on the substrate, which may be done by grit blasting, chemical etching, or mechanical means. Once profiled, the surface is coated with the disclosed alloy using any of a variety of thermal spray processes, such as High Velocity Oxy-Fuel (HVOF), Twin Wire Arc Spray (TWAS), Cold Spray, and Kinetic Metallization. Each of these different thermal spray processes is well known to those of skill in the art. In one embodiment, the utilized spray gun may be traversed along a cylindrical object where the object is rotating in a fixture such as a lathe or riding on pipe rollers. Traversing of the spray gun may be done manually by a human operator, automatically by robot, or by affixing the gun to a traversing mechanism. The disclosed coating may be applied to a room temperature substrate or the substrate may be pre-heated to approximately 200-400 degrees Fahrenheit.

As discussed above, prior art coatings develop micro-cracks in the coating, some of which may extend to the surface of the coating. To address these cracks, conventional techniques typically paint or treat the coating surface with a low surface tension liquid to penetrate and seal the cracks. In one embodiment, the disclosed thermal spraying process does not require this subsequent treatment of the coating because it has no micro-cracks that open to the surface, so there is no path to absorb the low viscosity sealing liquids. In other words, the disclosed embodiment does not require a subsequent sealing step of the resultant thermally sprayed coating as is typical in conventional techniques.

The thickness of the thermal spray coating varies based on the desired characteristics of the coating (wear resistance, impact resistance corrosion resistance, etc.) and the intended application of the coated tool/substrate. The tool being coated and the particular application of the tool will dictate the coating thickness. For many of the tests disclosed in the present application the substrate/tool was conventional 4″ drill pipe. While typically conventional coatings may be approximately 0.015″ thick, the disclosed coating can be applied both thinner and thicker as required. In one embodiment, the total coating thickness may be generated in multiple passes. In still other embodiments, a first layer of the coating may have a first composition (with a first thickness), while a second layer may have a second composition (with a second thickness). In one embodiment, the coating may be applied in thick deposits exceeding 0.100″, although ranges in the amount between 0.020″ up to 3.0″ are possible. The coating thickness (and/or each separate layer of the coating) may be relatively thin such as between 0.002″ to 0.020″, or bigger between 0.020″ to approximately 0.100″, or even greater thicknesses such as approximately 0.35″, 0.50″, or more. For example, U.S. Pat. No. 7,487,840 (the “840 Patent”) discloses an iron based coating that is at least 0.100″ thick. For the present disclosure, the disclosed coating and/or thermally sprayed layer may be less than 0.100″ thick (such as approximately 0.090″ or less), approximately 0.100″ thick, or greater than 0.100″ thick. In some embodiments, the layer of metallic material has a thickness of between about 0.010 inches and 0.10 inches, a thickness of between about 0.10 inches and 1.0 inches, or a thickness of between about 1.0 inches and 3.0 inches. In some embodiments, as is known in the art, multiple passes of thermal spray may be applied to the tool to create the desired thickness of coating and/or thermal spray layers. For example, 5 to 300 passes of thermal spray layers may be needed to create the desired thickness.

Examples/Tests

New Alloys 1-4 (as disclosed above) were applied to a sample substrate using conventional thermal spray processes. In particular, the thermal spray process was a twin-wire thermal spray as generally disclosed in U.S. Pat. No. 7,487,840. The substrate was the same for each of the samples and is a substantially iron based material similar to what is found on drill pipe utilized in the industry.

Among other tests, the Applicant performed a wear resistance test on each of the alloys. For the purposes of this disclosure, wear resistance is abrasive wear per ASTM G-65, weight loss in 6,000 revolutions, grams. According to this test, Alloys 1-4 had the following wear resistance values: 0.53, 0.50, 0.70, and 0.34, respectively. Thus, Alloy 3 had the lowest wear resistance and Alloy 4 had the highest wear resistance.

Further, various cross-sectional cuts of the thermally sprayed substrates were analyzed by a scanning electronic microscope (SEM) for each of these alloys. In particular, the cross-sectional views were captured at various magnifications to analyze the bonding and presence of cracks of the thermally sprayed layer to the surface of the drill pipe. These images are illustrated in FIGS. 3A-3D. These figures illustrate that the conventional alloys result in many micro-cracks, while the disclosed alloys of the present application provide little to no micro-cracks.

FIG. 3A shows a cross-sectional view of a layer 310 of Alloy 1 at a magnification of 444×. As illustrated, there are only a few micro-cracks, and then only through certain splats. For example, FIG. 3A shows micro-cracks 311 and 313. For the purposes of this disclosure, a “droplet” is molten and delivered through the air to a substrate, and a “droplet” becomes a “splat” on impact with the substrate. FIG. 3B shows a cross-sectional view of a layer 320 of Alloy 2 at a magnification of 444×. As illustrated, there are minimal micro-cracks. FIG. 3B shows micro-cracks 321. FIG. 3C shows a cross-sectional view of a layer 330 of Alloy 3 at a magnification of 444×. As illustrated, there are no visible micro-cracks. FIG. 3D shows a cross-sectional view of a layer 340 of Alloy 4 at a magnification of 444×. As illustrated, there are various micro-cracks running through the splats as well as along the splat boundaries. For example, micro-cracks 341, 343, and 345 run through the splat and/or splat boundaries.

FIGS. 4A-4C show various elemental compositions in a black strip of a thermal spray and substrate utilizing Alloy 3. In particular, FIG. 4A illustrates the elemental compositions in the base material of the substrate after being thermally sprayed with Alloy 3, FIG. 4B illustrates the elemental compositions at the interface between the base material of the substrate and the thermal spray droplets of Alloy 3, and FIG. 4C illustrates the elemental compositions in the thermal spray of Alloy 3 after spraying. The black strips illustrate various diffusion amounts of the elements within the thermal spray across the interface boundary and within the base material of the substrate based on the Energy Dispersive X-Ray Spectroscopy (EDS) result. For example, looking at boron, the thermal spray droplet has a wt % of approximately 24.5 wt %, the boron level at the interface is approximately 15.8 wt %, and the boron level in the base material (e.g., on the other side of the boundary with the thermal spray droplets) is approximately 10.5 wt %. While this method of measuring is qualitative rather than quantitative, these figures clearly show that there is diffusion of boron (and other elements) between the splats and the base material. In other words, these numbers do not show the precise amount of boron in each sample but a progression from a very high number in the sprayed splats to a lower number at the interface boundary and even a lower number in the substrate itself. While it is recognized that SEM and EDS is qualitative and not quantitative, the differential boron across the boundary area is evident in FIGS. 4A-4C.

FIG. 5A illustrates a cross-sectional view of a thermally sprayed sample of Alloy 4 at a magnification of 1200×. As illustrated, FIG. 5A shows micro-crack 511 within the substrate. For testing purposes, this substrate was exposed to chlorine. FIG. 5B shows the elemental compositions in a black strip at the interface point illustrated in FIG. 5A, and more particularly proximate to micro-crack 511. Further, FIG. 5B shows the incursion of chlorine deep down in micro-crack 511. In time, this crack (in connection with the chlorine and other corrosive agents) may result in a coating failure by corrosion and will produce a result similar to that viewed in FIG. 1B. Thus, elimination and/or minimization of cracks is highly advantageous for thermally sprayed deposits.

As described and illustrated above, the novel alloys described in the present disclosure minimize and/or eliminate micro-cracks in the thermally sprayed layer. This is a significant advancement over prior art. Further, Alloy 3 has no visible micro cracks, which greatly improves corrosion resistance and the overall strength of the spray. For the alloys that do have relatively few micro-cracks, it is desired that these micro-cracks go through only a single splat (which is the case, see, e.g., FIGS. 3A, 3B, 3D) as opposed to long running cracks that go through several splats and often also run along the splat boundaries as found in conventional thermal spray coatings. Based on the above tests, the disclosed alloys enable thick deposits (e.g., greater than 0.100″) to be made without (or at least minimal) internal cracks with an iron based alloy. Further, it can be readily demonstrated that other iron based coatings with abrasive wear rates of 0.70 grams weight loss or lower will have micro-cracks which limits their utility on applications such as mud motors and drill pipe where rotational flexing, torsion and impact can be severe. In one embodiment, the disclosed alloys have been proven to be sufficiently robust and wear resistant to be applied successfully to the hard band area of tool joints on drill pipe.

In one embodiment, the disclosed alloy compositions may be used in conjunction with an exothermic reaction, as described in U.S. patent application Ser. No. 16/351,155, filed on Mar. 12, 2019, incorporated herein by reference. Of course, the disclosed alloy may or may not be applied with such an exothermic reaction. For example, iron oxide and aluminum may be utilized (such as by powdered elements within a cored wire) to create an exothermic reaction by the following formula: Fe₂O₃+2Al→Al₂O₃+2Fe+heat. In one embodiment, the iron oxide (preferably Fe₂O₃) and aluminum (Al), in the correct mesh sizes, together decompose in the arc of a twin wire arc spray process and generate an exothermic reaction. Aluminum oxide (Al₂O₃) and iron (Fe) are the resultant forms, plus a significant amount of heat. This exothermic reaction super heats the droplets resulting in greater alloy mixing and melting/bonding time for the desired solidification structures to form. According to known methods using standard enthalpy values, the above exothermic reaction produces approximately −850 kJ/mol.

In one embodiment, for this reaction to initiate and continue both during the flight of the elements towards the substrate and even after colliding with the substrate, the mesh sizes of the iron oxide and aluminum particles should be small. A small particle size allows for a more even distribution in the powder core. In one embodiment, an effective mesh size for the aluminum and iron oxide particles is approximately 30 microns or more than 30 microns, but in other embodiments may be less than 30 microns or between 10-20 microns. In one embodiment, the aluminum particles (or other active elements) should not be heavily oxidized, as any amount of oxidation retards melting and availability for the reaction to rapidly take place.

In other embodiments, the exothermic reaction may also be accomplished by using other elements besides iron oxide and/or aluminum. In general, the droplets of the thermal spray coating may be superheated by the heat given off by any exothermic reaction of an oxidizer and a fuel, which produces heat and a byproduct (i.e., OXIDIZER+FUEL→PRODUCTS+HEAT). In one embodiment, the oxidizer (or oxidizing element) may be any number of oxides, such as oxides of iron, copper, nickel, bismuth, boron, silicon, chromium, manganese, or lead. In one embodiment, the fuel may be considered as an active element, and may consist of aluminum, magnesium, lithium, potassium, silicon, boron, titanium, or zinc. For the present disclosure, the oxidizing element and the active element may be considered as a plurality of reactants that form the exothermic reaction.

In one embodiment, the present disclosure incorporates an exothermic reaction to a thermal spray technique to facilitate transfer of sprayed metallic material from a cored wire onto an exterior portion of a substrate, thereby forming a thermal spray coating on the substrate. In one embodiment, a thermal spray method and system may utilize an exothermic reaction in the thermal spray composition itself to create and maintain a higher droplet temperature. The use of an exothermic reaction minimizes and/or eliminates the presence of micro-cracks in the coating. The elimination and/or minimization of micro-cracks improves impact and fatigue strength of the coating and lessens the opportunity for corrosive failure of the coating. In one embodiment, the use of an exothermic reaction greatly improves bond strength of the coating, bond strength between the coating and the substrate, and bond strength between solidified droplets (splats) of the applied metallic material. In one embodiment, the use of an exothermic reaction improves bonding between powdered elements within a cored wire and the cored wire's outer sheathing (which is generally substantially solid). In one embodiment, the use of an exothermic reaction improves alloy homogeneity and diffusion of boron and/or carbon. In one embodiment, the use of an exothermic reaction results in metallurgical bonding between the thermally sprayed droplet and the base material.

As mentioned above, FIGS. 4A-4C show various elemental compositions in a black strip of a thermal spray and substrate utilizing Alloy 3, which includes a lithium component of the alloy. In particular, the utilized cored wire composition included powdered elements of lithium in addition to aluminum and iron oxide, along with boron and carbon as described herein. This coating is referred to as FABLi, as it uses a lithium reactive element. The use of and benefits related to lithium are described in greater detail above. The inner core is approximately 30 weight percent of the wire and the outer sheath (steel) is approximately 70 weight percent of the wire. This coating was applied to a steel test sample via conventional thermal spray techniques as described above. The alloy is important not only because of the lithium component but because of the exothermic reaction created by the selected alloy ingredients. As mentioned above, FIGS. 4A-4C illustrate various elemental compositions of the FABLi alloy in relation to the coating of a substrate. FIG. 4A shows the composition in a base material after being thermally sprayed with the FABLi alloy, FIG. 4B shows the composition at the interface between the base material and the FABLi alloy coating, and FIG. 4C shows the composition of the FABLi alloy coating after being thermally sprayed on the base material. The compositions illustrated in these figures show the increased diffusion of boron and carbon as a result of the exothermic reaction. For example, FIG. 4C shows that the coating has an approximate weight percentage of 24.5% boron and 4.0% carbon, FIG. 4B shows that the interface has approximately 15.8% boron and 4.0% carbon, and FIG. 4A shows that the base material has approximately 10.5% boron and 2.8% carbon. Thus, increased boron and carbon diffusion (as measured by SEM) may be caused by any exothermic reaction that creates sufficient enough heat. It is noted that lithium is not indicated in these elemental composition breakdowns because SEM does not have the capability to measure and/or test for lithium.

FIGS. 6A and 6B illustrate another visual test comparing a conventional alloy with an alloy of the present disclosure that utilizes an exothermic reaction. FIG. 6A illustrates a cross-sectional view of a thermal spray coating of a conventional alloy (i.e., an alloy that does not utilize an exothermic reaction) on a steel block test sample, at a magnification of approximately 69×. FIG. 6A illustrates base material 601, interface 603, thermal spray coating 605, and cracks 607 within thermal spray coating 605. FIG. 6B illustrates a cross-sectional view of a thermal spray coating of an alloy that utilizes an exothermic reaction according to one embodiment of the present disclosure, on a steel lock test sample at a magnification of approximately 69×. FIG. 6B illustrates the FABLi alloy (e.g., Alloy 3), which utilizes aluminum and iron oxide and lithium as described previously. FIG. 6B illustrates base material 651 (which is the same base material as shown in FIG. 6A), interface 653, and thermal spray coating 655. As easily seen, there are no cracks present in coating 655. Thus, comparing FIGS. 6A and 6B shows that the disclosed composition using an exothermic reaction produces a layer and/or coating that forms substantially no cracks.

In one embodiment, the use of the novel alloy compositions as disclosed herein results in metallurgical bonding between the thermally sprayed droplet and the base material, which is very unusual in conventional thermal sprays. In typical thermal spray applications, a layer of metallic material is thermally sprayed onto a substrate such that the coating does not metallurgically affect the base material. For example, U.S. Pat. No. 7,487,840 discloses a wear-resistant layer that is sprayed onto a downhole component independent of metallurgical changes to a base material of the downhole component. Likewise, U.S. Pat. No. 9,920,412 discloses a coating that that does not substantially alter the metallurgical properties of the substrate. In contrast, for at least some exothermic reactions as described herein, metallurgical bonding occurs at the interface between the base material and the coating. In general, metallurgical bonding is chemical bonding, which is contrasted to mechanical bonding that is typical for thermally sprayed allows; this comparison might be likened to a bolted connection versus a welded connection. Metallurgical bonding is the result of chemical bonding that occurs between a substrate and coating areas that are in close contact or diffused evenly. Metallurgical bonding is essentially non-existent in thermal spray deposits as normal thermal spray deposits are mechanically interlocked into the roughened or profiled surface on the substrate and subsequent droplets follow this profile as they land on the surface. These mechanical bonds are not nearly as strong as a true metallurgical bond.

FIG. 7 shows such an example of metallurgical bonding of a thermal spray coating to a substrate. In particular, FIG. 7 illustrates a cross-sectional view of a thermal spray coating on a steel test sample using an exothermic reaction according to one embodiment of the present disclosure, at a magnification of approximately 7000×. The composition is the same FABLi alloy as described above. The substrate is A36 steel test block. FIG. 7 illustrates base material 701 (steel), interface 711, and thermal spray coating 721. Metallurgical bonding 710 is found at interface 711, which is the bonding area between the base material and the thermal spray coating. As explained above, this metallurgical bonding is unexpected and not present in conventional thermally sprayed alloys and techniques. Metallurgical bonding is well known to be much superior in strength and ductility to merely mechanical bonds, and is thus desirable in many situations.

In one embodiment, the disclosed alloy compositions may be used in conjunction with one or more reinforcing structures, as described in U.S. Patent Publication No. 2019/0010598, incorporated herein by reference. The use of reinforcing structures in thermal spray techniques is analogous to using re-bar in concrete. For example, a thermally sprayed layer of the alloy compositions described herein may comprise reinforcing structures such as whiskers and/or wires. The reinforcing structure may be a metallic or non-metallic wire, filament, whisker, mesh, or similar structure and may be coupled to the substrate before or during the thermal spray process, thereby embedding the reinforcing structure(s) into the resulting thermal spray matrix. The type, material, size, shape, and application technique of the reinforcing structure is variable based upon the desired characteristics of the ultimate coating. For example, the spray method may further comprise coupling the one or more reinforcing structures to the external surface during the thermally spraying step. The spray method may further comprise coupling the one or more reinforcing structures to the external surface prior to the thermally spraying step. The method may further comprise spraying the one or more reinforcing structures onto the external surface by compressed gas at the same time or prior to the thermally spraying step. The method may further comprise wrapping the one or more reinforcing structures around at least a portion of the substrate prior to the thermally spraying step.

All of the methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the apparatus and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. In addition, modifications may be made to the disclosed apparatus and components may be eliminated or substituted for the components described herein where the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope, and concept of the invention.

Many other variations in the system are within the scope of the invention. For example, the alloy may or may not include titanium, lithium, manganese, silicon, nickel, molybdenum, and/or chromium. Lithium, aluminum, and/or magnesium may be used as a fluxing agent and/or reactive ingredient in the alloy composition. The tool to be coated may be a downhole component or other tool used in the oil and gas industry, or may be applied to any object or tool that needs an increased impact and/or wear resistant layer or friction reduction layer or corrosion resistant layer, such as in the aviation and marine industries, as well as dredge pups, cable sheaves, and helicopter landing runners, among others. The disclosed technology is applicable to both wear resistant overlays as well as corrosion resistant applications. An exothermic reaction may or may not be utilized, and reinforcing wire may or may not be utilized. Likewise, metallurgical bonding may or may not occur between droplets of the thermally sprayed material and/or the thermally sprayed material and the substrate's base material. It is emphasized that the foregoing embodiments are only examples of the very many different structural and material configurations that are possible within the scope of the present invention.

Although the invention(s) is/are described herein with reference to specific embodiments, various modifications and changes can be made without departing from the scope of the present invention(s), as presently set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention(s). Any benefits, advantages, or solutions to problems that are described herein with regard to specific embodiments are not intended to be construed as a critical, required, or essential feature or element of any or all the claims.

Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The terms “coupled” or “operably coupled” are defined as connected, although not necessarily directly, and not necessarily mechanically. The terms “a” and “an” are defined as one or more unless stated otherwise. The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”) and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a system, device, or apparatus that “comprises,” “has,” “includes” or “contains” one or more elements possesses those one or more elements but is not limited to possessing only those one or more elements. Similarly, a method or process that “comprises,” “has,” “includes” or “contains” one or more operations possesses those one or more operations but is not limited to possessing only those one or more operations. 

What is claimed is:
 1. A composition for thermally spraying to a substrate, the composition comprising iron alloyed with the following components: at least 0.3 wt % carbon; at least 5.0 wt % boron; and at least 0.5 wt % of a fluxing agent selected from the group consisting of aluminum, magnesium, or lithium.
 2. The composition of claim 1, wherein the composition comprises at least 0.5 wt % lithium.
 3. The composition of claim 1, wherein the composition comprises at least 5.0 wt % lithium.
 4. The composition of claim 1, wherein the composition comprises at least 0.5 wt % magnesium.
 5. The composition of claim 1, wherein the composition comprises at least 5.0 wt % magnesium.
 6. The composition of claim 1, wherein the composition comprises at least 0.5 wt % aluminum.
 7. The composition of claim 1, wherein the composition comprises at least 2.0 wt % aluminum and at least 0.5 wt % lithium.
 8. The composition of claim 1, wherein the composition further comprises: at least 0.5 wt % carbon; and at least 7.0 wt % boron.
 9. The composition of claim 1, wherein the composition further comprises: at least 2.0 wt % aluminum; at least 1.0 wt % nickel; and at least 1.0 wt % titanium.
 10. The composition of claim 1, further comprising a plurality of reactants that create an exothermic reaction when ignited and thermally sprayed onto the substrate.
 11. The composition of claim 1, wherein the amount of the fluxing agent is effective to prevent oxide film formation on droplets of the composition during thermal spray.
 12. The composition of claim 1, wherein the amount of the fluxing agent is effective to increase droplet temperature of the composition during thermal spray.
 13. The composition of claim 1, wherein the amount of the fluxing agent is effective to cause metallurgical bonding between a layer of sprayed metallic material and the substrate.
 14. The composition of claim 1, wherein the composition is effective to prevent micro-cracks from forming in the thermal spray.
 15. The composition of claim 1, wherein the composition is effective to reduce the amount of micro-cracks within a layer of sprayed metallic material on the substrate.
 16. The composition of claim 1, wherein the composition is effective to diffuse at least a portion of the carbon and boron to a base material of the substrate.
 17. A modified downhole component, comprising: a downhole component with an external surface; and a layer of metallic material that is thermally sprayed onto a portion of the external surface, wherein the layer of metallic material comprises a composition, at least prior to being sprayed, of at least 0.3 wt % carbon, at least 5.0 wt % boron, and at least 0.5 wt % of a fluxing agent selected from the group consisting of aluminum, magnesium, or lithium.
 18. The component of claim 17, wherein the composition comprises at least 2.0 wt % aluminum.
 19. The component of claim 17, wherein the composition comprises at least 0.5 wt % lithium.
 20. The component of claim 17, wherein the component is a drill pipe.
 21. The component of claim 17, wherein the component is a drill pipe tool joint.
 22. The component of claim 17, wherein the layer of metallic material has a thickness of between about 0.010 inches and 0.10 inches.
 23. The component of claim 17, wherein the layer of metallic material has a thickness of between about 0.10 inches and 1.0 inches.
 24. The component of claim 17, wherein the layer of metallic material has a thickness of between about 1.0 inches and 3.0 inches.
 25. The component of claim 17, wherein at least a portion of the carbon and boron has diffused from the layer of metallic material to a base material of the downhole component.
 26. The component of claim 17, wherein the layer of metallic material is resistant to micro-cracks.
 27. The component of claim 17, wherein the layer of metallic material comprises substantially no micro-cracks.
 28. The component of claim 17, wherein the layer of metallic material is at least partially metallurgically bonded to the downhole component.
 29. The component of claim 17, wherein the layer of metallic material is formed by an exothermic reaction.
 30. The component of claim 17, further comprising one or more reinforcing structures embedded within the layer of metallic material.
 31. The component of claim 30, wherein the one or more reinforcing structures comprises one or more continuous wires.
 32. The component of claim 30, wherein the one or more reinforcing structures comprises a plurality of whiskers.
 33. A modified downhole component, comprising: a downhole component with an external surface; and a layer of metallic material that is thermal sprayed onto a portion of the external surface, wherein the layer of material is at least partially metallurgically bonded to the downhole component.
 34. The component of claim 33, wherein the composition of the layer of material further comprises iron alloyed with the following components: at least 0.3 wt % carbon; at least 5.0 wt % boron; and at least 0.5 wt % of a fluxing agent selected from the group consisting of aluminum, magnesium, or lithium.
 35. The component of claim 34, wherein the amount of the fluxing agent is effective to cause the metallurgical bonding.
 36. The component of claim 33, wherein the composition comprises a plurality of reactants that create an exothermic reaction when ignited and thermally sprayed onto the substrate, wherein the composition comprises at least 0.5 wt % of a lithium compound.
 37. A method for thermally applying a coating to a substrate, comprising: thermally spraying metallic material on an external surface of a substrate to form a thermal spray layer on the substrate, wherein the material, at least prior to being sprayed, comprises iron alloyed with the following components: at least 0.3 wt % carbon; at least 5.0 wt % boron; and at least 0.5 wt % of a fluxing agent selected from the group consisting of aluminum, magnesium, or lithium.
 38. The method of claim 37, further comprising embedding one or more reinforcing structures into the thermal spray layer.
 39. The method of claim 38, further comprising spraying the one or more reinforcing structures onto the external surface of the substrate by compressed gas.
 40. The method of claim 37, further comprising metallurgically bonding the sprayed metallic material with the substrate.
 41. The method of claim 37, further comprising metallurgically bonding together droplets of the sprayed metallic material.
 42. The method of claim 37, further comprising diffusing boron and carbon between the thermal spray layer and the substrate.
 43. The method of claim 37, further comprising creating an exothermic reaction during the thermal spray step.
 44. The method of claim 43, further comprising igniting a plurality of reactants within a cored wire to create the exothermic reaction.
 45. The method of claim 43, further comprising increasing droplet temperature of the sprayed metallic material based on the fluxing agent.
 46. The method of claim 37, further comprising forming a layer of thermally sprayed material on the substrate that is between about 0.010 inches and 0.10 inches.
 47. The method of claim 37, further comprising forming a layer of thermally sprayed material on the substrate that is at least 0.1″ thick.
 48. The method of claim 37, further comprising forming a layer of thermally sprayed material on the substrate that is at least 1.0″ thick.
 49. The method of claim 37, further comprising preventing oxide film formation on droplets of the sprayed metallic material. 